fix: various security fixes (#38406)

Addresses a batch of privately reported security issues, grouped by
area:

- **SSRF** - migration PR-patch/asset fetches, OAuth2 avatar & OpenID
discovery, pull-mirror URL re-validation, and the outbound proxy path.
- **Access-token scope** - prevent scope escalation on token creation;
keep public-only tokens confined (feeds, packages, Actions listings,
star/watch lists, limited/private owners).
- **Access control / disclosure** - go-get default-branch leak, webhook
authorization-header leak, watch clearing on private transitions,
label/attachment scoping.
- **Denial of service** - input bounds for npm dist-tags, Debian control
files, Arch file lists, and SSH keys.

### 📌 Attention for site admins

Not breaking - existing configs keep working - but two changes are worth
a look:

- **New SSRF protection** Outbound requests (migrations, OAuth2 avatars,
OpenID discovery, pull mirrors, proxy path) are now validated against
the allow/block host lists. If your instance legitimately reaches
internal hosts, you may need to add them to
`[security].ALLOWED_HOST_LIST` (and the relevant `ALLOW_LOCALNETWORKS`
settings).
- **Deprecation** `[webhook].ALLOWED_HOST_LIST` is deprecated and will
be removed in a future release. Use `[security].ALLOWED_HOST_LIST`
instead; the old key still works for now.

---------

Co-authored-by: TheFox0x7 <thefox0x7@gmail.com>
Co-authored-by: techknowlogick <techknowlogick@gitea.io>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: Zettat123 <zettat123@gmail.com>

tests/integration/feed_user_test.go

@@ -8,6 +8,7 @@ import (
 	"net/http"
 	"testing"
 
+	auth_model "gitea.dev/models/auth"
 	"gitea.dev/tests"
 
 	"github.com/stretchr/testify/assert"
@@ -58,3 +59,51 @@ func TestFeedUser(t *testing.T) {
 		})
 	})
 }
+
+// TestFeedUserPublicOnlyToken ensures a public-only API token cannot surface a user's
+// private activity through their profile feed, even when authenticated as the owner.
+func TestFeedUserPublicOnlyToken(t *testing.T) {
+	defer tests.PrepareTestEnv(t)()
+
+	// user2 has activity on the private repo user2/repo2
+	const privateMarker = "user2/repo2"
+
+	// a normal read:user token authenticated as the owner sees private activity
+	fullToken := getUserToken(t, "user2", auth_model.AccessTokenScopeReadUser)
+	reqFull := NewRequest(t, "GET", "/user2.rss")
+	reqFull.SetBasicAuth("user2", fullToken)
+	respFull := MakeRequest(t, reqFull, http.StatusOK)
+	assert.Contains(t, respFull.Body.String(), privateMarker)
+
+	// a public-only token must not surface the private activity
+	publicOnlyToken := getUserToken(t, "user2", auth_model.AccessTokenScopeReadUser, auth_model.AccessTokenScopePublicOnly)
+	reqPublicOnly := NewRequest(t, "GET", "/user2.rss")
+	reqPublicOnly.SetBasicAuth("user2", publicOnlyToken)
+	respPublicOnly := MakeRequest(t, reqPublicOnly, http.StatusOK)
+	assert.NotContains(t, respPublicOnly.Body.String(), privateMarker)
+}
+
+// TestProfileActivityPublicOnlyToken ensures the HTML profile activity tab does not
+// surface a user's private activity to a public-only API token, mirroring the RSS/Atom
+// guard. The /{username} route is AllowBasic, so a public-only PAT used as the Basic
+// password must still be downgraded even for the feed owner.
+func TestProfileActivityPublicOnlyToken(t *testing.T) {
+	defer tests.PrepareTestEnv(t)()
+
+	// user2 has activity on the private repo user2/repo2
+	const privateMarker = "user2/repo2"
+
+	// a normal read:user token authenticated as the owner sees private activity
+	fullToken := getUserToken(t, "user2", auth_model.AccessTokenScopeReadUser)
+	reqFull := NewRequest(t, "GET", "/user2?tab=activity")
+	reqFull.SetBasicAuth("user2", fullToken)
+	respFull := MakeRequest(t, reqFull, http.StatusOK)
+	assert.Contains(t, respFull.Body.String(), privateMarker)
+
+	// a public-only token must not surface the private activity
+	publicOnlyToken := getUserToken(t, "user2", auth_model.AccessTokenScopeReadUser, auth_model.AccessTokenScopePublicOnly)
+	reqPublicOnly := NewRequest(t, "GET", "/user2?tab=activity")
+	reqPublicOnly.SetBasicAuth("user2", publicOnlyToken)
+	respPublicOnly := MakeRequest(t, reqPublicOnly, http.StatusOK)
+	assert.NotContains(t, respPublicOnly.Body.String(), privateMarker)
+}